Millimeter and sub-millimeter wave portal

ABSTRACT

In accordance with one embodiment of the present invention, a millimeter or sub-millimeter wave portal system is provided. Generally, the portal system comprises an electrooptic source and one or more millimeter or sub-millimeter wave detectors. The electrooptic source comprises an optical signal generator, optical switching and encoding circuitry, and one or more optical/electrical converters. Additional embodiments are disclosed and claimed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/865,498 (OPI 0032 MA), filed Nov. 13, 2006. The presentapplication is also related to commonly assigned U.S. patent applicationSer. No. ______ (OPI 0033 PA), which application has been filedconcurrently herewith.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to the utilization of millimeter andsub-millimeter waves to sense, identify, locate, image, or otherwisedetect objects within a field of view. More specifically, the presentinvention relates to the design of a portal system that utilizesmillimeter and sub-millimeter waves to detect the presence of particulartypes of objects passing through one or more portals. In accordance withone embodiment of the present invention, a millimeter or sub-millimeterwave portal system is provided. Generally, the portal system comprisesan electrooptic source and one or more millimeter or sub-millimeter wavedetectors. The electrooptic source comprises an optical signalgenerator, optical switching and encoding circuitry, and one or moreoptical/electrical converters. Additional embodiments are disclosed andclaimed.

The present invention also relates to the design and operation of afrequency selective electrooptic source having utility beyond theaforementioned security portal embodiments. In accordance with oneembodiment of the present invention, the electrooptic source comprisesan optical signal generator, optical circuitry, and at least oneoptical/electrical converter wherein the optical signal generatorcomprises a plurality of optical outputs characterized by distinctoutput frequencies and the optical circuitry is configured to permit theselection and combination of different ones of the distinct-frequencyoptical outputs to generate a modulated optical signal, which isconverted to a millimeter or sub-millimeter wave.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of specific embodiments of thepresent invention can be best understood when read in conjunction withthe following drawings, in which:

FIG. 1 is a schematic illustration of a millimeter or sub-millimeterwave portal system according to one embodiment of the present invention;

FIG. 2A is a schematic illustration of an electrooptic source accordingto one embodiment of the present invention;

FIG. 2B is a schematic illustration of an electrooptic source accordingto an embodiment of the present invention in the context of a planarlightwave circuit;

FIG. 2C is a skewed schematic illustration of a waveguide configurationaccording to one embodiment of the present invention;

FIG. 2D is a graphic illustration of an operating mode of anelectrooptic source according to one embodiment of the presentinvention;

FIGS. 3A-3D are graphic illustrations of the time-domain response of asideband generator according to one embodiment of the present inventionwith drive voltage amplitudes equal to V_(π)/4, V_(π)/2, V_(π), and2V_(π);

FIG. 4 is a graphic illustration of the relationship between theamplitude of the odd numbered harmonics and the normalized drivevoltage, V_(m)/V_(π) in the context of a sideband generator according toone embodiment of the present invention;

FIGS. 5A-5C are graphic illustrations of an unmodulated optical signaland an optical spectrum at the output of a sideband generator accordingto an embodiment of the present invention with V_(m)=Vπ and V_(m)=2Vπ;

FIG. 6 is a schematic illustration of the operation of an optical filterand signal combiner according to one embodiment of the presentinvention;

FIG. 7 is a schematic illustration of the operation of data encoderaccording to one embodiment of the present invention;

FIGS. 8A-8D are graphic illustrations of the time-domain response of asideband generator according to another embodiment of the presentinvention with drive voltage amplitudes equal to V_(π)/4, V_(π)/2,V_(π), and 2V_(π);

FIG. 9 is a graphic illustration of the relationship between theamplitude of the even numbered harmonics and the normalized drivevoltage, V_(m)/V_(π) in the context of a sideband generator according toone embodiment of the present invention;

FIG. 10 is a schematic illustration of a phase modulator configurationaccording to an embodiment of the present invention where a phasemodulator is used as a sideband generator;

FIGS. 11A-11D are graphic illustrations of an optical spectrum at theoutput of a phase modulator sideband generator according to anembodiment of the present invention with V_(m)=0.01Vπ, V_(m)=0.50Vπ,V_(m)=Vπ, and V_(m)=2.04Vπ;

FIG. 12 is a schematic illustration of an electrooptic antenna assemblyaccording to one embodiment of the present invention;

FIG. 13 is a schematic cross sectional illustration of the active regionof the antenna assembly illustrated in FIG. 12;

FIGS. 14 and 15 are schematic illustrations of two of the manyalternative tapered slot antenna configurations for use in embodimentsof the present invention;

FIG. 16 is a schematic plan view of an antenna assembly according toanother embodiment of the present invention;

FIG. 17 is a schematic cross sectional illustration of the active regionof the antenna assembly illustrated in FIG. 4;

FIGS. 18 and 19 are schematic illustrations of antenna assembliesconfigured as one-dimensional and two-dimensional focal plane arrays,respectively.

DETAILED DESCRIPTION

A schematic illustration of a millimeter or sub-millimeter wave portalsystem 1 according to one embodiment of the present invention isillustrated in FIG. 1. Generally, the portal system 1 comprises anelectrooptic source 10 and one or more millimeter or sub-millimeter wavedetectors 150. The electrooptic source comprises an optical signalgenerator 120, optical switching and encoding circuitry 130, and one ormore optical/electrical converters 140.

For the purposes of describing and defining the present invention, it isnoted that reference herein to millimeter and sub-millimeter wavesignals denote frequencies that are ≧30 GHz. The optical signalgenerator 120 is configured to generate a modulated optical signalcharacterized by a modulation frequency of at least about 30 GHz. Theoptical circuitry is configured to direct the modulated optical signalto one or more optical/electrical converters 140 via optical fibers,waveguides, or other suitable optical transmission lines 135. Eachoptical/electrical converter 140 is configured to convert the modulatedoptical signal to a millimeter or sub-millimeter wave 100 and direct themillimeter or sub-millimeter wave 100 in the direction of an object 200positioned within a field-of-view defined by one of the millimeter orsub-millimeter wave detectors 150. Each millimeter or sub-millimeterwave detector 150 is configured to convert reflections 110 of themillimeter or sub-millimeter wave from the object 200 to signalsrepresenting attenuation of the millimeter or sub-millimeter wave 100upon reflection from the object 200.

A variety of analysis schemes can be applied to the signals representingthe attenuation of the millimeter or sub-millimeter wave 100 uponreflection from the object 200 to determine whether a particular item ofinterest is present in or carried on the object 200. The details ofthese schemes can be gleaned from conventional or yet to be developedteachings related to millimeter or sub-millimeter wave detection. Forexample, and not by way of limitation, metallic or non-metallic objectsconcealed beneath clothing can be observed using millimeter wave (mmw)imaging by correlating the attenuation with the frequency-dependentattenuation or reflectivity of common materials like flannel, polyester,cotton, nylon, polycarbonate, human skin, etc.

In one embodiment of the present invention, if a mmw image is taken of aperson at a given frequency, the expected image of that same person at adifferent frequency can be reasonably well approximated, based solely onthe frequency dependence of the reflectivity of human skin. If theperson is carrying a concealed object, the expected image of that personat a second frequency will differ from the expected image, due to thedifferent reflectivity of the concealed object. This deviation betweenthe expected image and measured image at the alternate frequency can beused to indicate the presence of a concealed object without humaninterpretation of the image. Although the present invention is notlimited to the use of multiple mmw frequencies, the use of more than twofrequencies in the portal system of the present invention can reduce thenumber of false positives without sacrificing the ability to detectconcealed objects. For example, because the total reflected power at agiven frequency depends on the size and shape of the target as well asclothing worn and any concealed objects, the system can be configured tobe self-calibrating by programming the data collection and analysis unit160 to compare attenuation in the reflected signal at multiplefrequencies. The size and shape of the object 20 as well as the clothingcomposition can be removed as variables, by comparing the response ofthe target object 200 at the appropriate frequencies, leaving only thepresence of a concealed object to change the reflectance from theexpected frequency-dependent response.

The determination of the potential presence of a concealed object isperformed by the data collection and analysis unit 160. It is envisionedthat the multiple mmw security portals being served by the single mmwwaveform generator may have a common data analysis unit 160. Thepresence of a potential concealed object can then be signaled at theproper portal by a “beep” or other indicator, such as occurs withexisting magnetometers. Alternatively, mmw portals according to thepresent invention can be equipped with an array of detectors 150configured to generate an image of the object 200, in which casesuitable image processing software would need to be incorporated in thedata collection and analysis unit 160.

Typically, the field-of-view defined by the millimeter or sub-millimeterwave detectors 150 is such that the object 200 cannot pass through ornear a portal 170 of the portal system 100 without also passing throughthe field-of-view of a detector 150. In the illustrated embodiment, theportal 160 is configured as a walk-through portal including a pair ofmillimeter or sub-millimeter wave components 180 and a supplementaldetection component 190 operating as a conventional metal detector, oranother type of conventional or yet to be developed detector or imagingdevice suitable for use in a portal system. For the purposes of definingand describing the present invention, it is noted that reference hereinto a “portal” should be taken to cover a variety of structures orconfigurations suitable for object analysis including, but not limitedto, a doorway, gateway, entry, threshold, portico, station, terminal,passage, etc.

Although the optical signal generator 120 may take a variety ofconventional or yet to be developed forms suitable for generating amodulated optical signal, according to one embodiment of the presentinvention, the generator 120 comprises an electrooptic sidebandgenerator 20 and an optical filter 30, the structure of which isdescribed in detail below with reference to FIGS. 2-11. As is describedbelow with reference to FIGS. 2-11, in the case of the embodiment of thepresent invention illustrated in FIGS. 2A and 2B, where an arrayedwaveguide grating (AWG) is employed as the optical filter 30, each ofthe outputs of the generator 120 will carry a distinct optical frequencybecause the AWG comprises multiple frequency channels, each of which ischaracterized by a unique, relatively narrow bandwidth.

For example, in the case of a 25 GHz AWG, each output channel of the AWGhas a 3 dB bandwidth of about 25 GHz and is separated from adjacentchannels by 25 GHz. Accordingly, referring generally to the AWGstructure illustrated in FIG. 6, which is described in detail below, theoutput channel passing unmodulated light is designated as the centerchannel and each additional port is assigned a +/− port number denotingthe sequential frequency separation of the port from the center channel.In the case of the 25 GHz AWG, the center wavelength of the first porton the high frequency side of the center channel (port P1 ⁺) will be 25GHz above that of the center channel (P0), while the center wavelengthof the first port on the low frequency side of the center channel (portP1 ⁻) will be 25 GHz below that of the center channel (P0). Since portP1 ⁺ has a 3 dB bandwidth of 25 GHz, this channel would pass wavelengthsfrom λ₀+12.5 GHz to λ₀+37.5 GHz, where λ₀ represents the wavelength ofthe center channel. Similarly, the center wavelength of the second porton the high frequency side of the center channel (port P2 ⁺) will be 50GHz above that of the center channel (P0), while the center wavelengthof the second port on the low frequency side of the center channel (portP2 ⁻) will be 50 GHz below that of the center channel (P0). Since portP2 ⁺ also has a 3 dB bandwidth of 25 GHz, this channel would passwavelengths from λ₀+37.5 GHz to λ₀+62.5 GHz. Accordingly, the distinctfrequencies created by the sideband generator need not match thespecific center wavelengths of the AWG channels. Rather, the design ofthe AWG and the configuration of the sideband generator merely need toresult in a configuration where the distinct frequencies created by thesideband generator are passed through separate ones of the AWG channels.

In FIG. 2C, a plurality of waveguides 55 and optical couplers 58 areformed on a waveguide substrate to define a series of input channels Isuitable for coupling to the output channels of the AWG, and a series ofoutput channels O configured to transmit respective signal pairscombined by the optical couplers 58. In the illustrated configuration,the center channel signal is directed to a suitable optical dump D whilethe first, second, and third order sidebands are combined and directedto the output channels O. These combined MMW optical carriers can bedirected to additional optical switching circuitry to ensure that thecorrect carrier is encoded and/or directed to the suitable O/Econverters for transmission of MMW signals.

An example of the manner in which the optical signal generator 120 canbe driven is illustrated in the table below and in FIG. 2D. The opticalsignal generator 120 can be driven at, e.g., 17.5 GHz, to generate firstorder sidebands spaced apart from each other by about 35 GHz. Morespecifically, by definition, each first order sideband is spaced fromthe drive signal by 17.5 GHz and, as such, the first order side bandsare spaced from each other by twice that amount, i.e., 35 GHz. Each ofthese first order sidebands is directed to distinct generator outputs bythe optical filter 30 and can be selectively combined by the switchingcircuitry 130 to yield continuous-wave Ka-band optical modulation at 35GHz. Selection and combination of second, third, or fourth ordersidebands of the 17.5 GHz drive frequency would yield optical modulationof 70 GHz (V-band), 105 GHz (W-band), and 140 GHz (F-band),respectively. This linear relationship is illustrated in FIG. 2D for thefirst, second, third, and fourth-order side bands over a drive frequencyrange extending from about 10 GHz to about 22 GHz.

Ka Band Operation W-Band Operation F-Band Operation MMW Carrier 35 GHz94 GHz 140 GHz Frequency Drive Frequency 17.5 GHz 15.67 GHz 17.5 GHzSidebands Used +/−1 +/−3 +/−4 Sideband λ₀ + 17.5 GHz λ₀ + 47 GHz λ₀ + 70GHz Wavelengths λ₀ − 17.5 GHz λ₀ − 47 GHz λ₀ − 70 GHz AWG Ports Used P1⁺(λ₀ + 12.5 GHz to P2⁺ (λ₀ + 37.5 GHz to P3⁺ (λ₀ + 62.5 GHz to (25 GHzAWG) λ₀ + 37.5 GHz) λ₀ + 62.5 GHz) λ₀ + 87.5 GHz) P1⁻ (λ₀ − 12.5 GHz toP2⁻ (λ₀ − 37.5 GHz to P3⁻ (λ₀ − 62.5 GHz to λ₀ − 37.5 GHz) λ₀ − 62.5GHz) λ₀ − 87.5 GHz)

The sideband generation and illustrated in FIGS. 2C and 2D, and in thetable above, merely involves the combination of like order sidebands,e.g., +/−1, +/−3, +/−4 etc. However, it is contemplated that the opticalcircuitry 130 can be configured to select and combine different ones ofthe distinct-frequency optical outputs to yield a variety of distinct,continuous-wave, modulated optical signal outputs. For example,according to one embodiment of the present invention, a series ofwaveguides and waveguide combiners can be formed on a single waveguidesubstrate and can be configured to facilitate selection and combinationof distinct-frequency optical outputs from different order sidebands,e.g., +4/0, +1/−2; −3/−5, etc. As a result, the optical signal generator120 and optical circuitry according to this embodiment of the presentinvention cooperate to introduce frequency selection capabilities in theelectrooptic source 10.

The crossing waveguide configuration illustrated in FIG. 2C isparticularly useful where a tri-band electrooptic source is desired.Specifically, if the sideband generator 20 illustrated in FIG. 2A isdriven hard enough, each of the input channels I of the crossingwaveguide configuration illustrated in FIG. 2C will carry a distinctsideband. These distinct sidebands can be combined as dictated by theconfiguration of the waveguides 55 and the optical couplers 58 to yieldthree frequency distinct MMW carrier signals, each of which can betransmitted via a separate output channel O. It is noted that the scaleof FIG. 2C has been skewed to provide increased separation between therespective waveguides 55. In addition, the configuration of therespective optical couplers is merely illustrated schematically.Finally, we note that the waveguides may cross in the manner illustratedin FIG. 2C, as long as the respective crossing angles are reasonablylarge to avoid optical interference.

In cases where the sideband generator 20 is merely driven hard enough tocreate a limited number of prominent sidebands, the center wavelength ofthe laser source 15 can be tuned to enhance frequency selection. Forexample, consider the case where the sideband generator merely createsprominent first and third order sidebands. If the wavelength of thelaser source 15 is tuned the center channel of the AWG, the waveguidenetwork 55 will generate only two frequency distinct MMW carriersignals, one corresponding to the +/−1 sidebands, and the other to the+/−3 sidebands. If the preferred MMW carrier signal actually correspondsto the +/−2 sidebands, the wavelength of the laser can be tuned suchthat it shifts to the +1 channel of the AWG and the +1 input channel ofthe waveguide network 55. As a result, the waveguide network 55 andoptical couplers 58 would combine the signals residing on the −3/+1channels and generate a MMW carrier corresponding to the −3/+1sidebands, which would be the equivalent of a combination of the +/−2sidebands.

Wavelength selection can also be achieved by varying the drive frequencyof the sideband generator. For example, as is further illustrated in thetable above and in FIG. 2D, the optical signal generator 120 can bedriven at, e.g., 15.67 GHz, to generate third order sidebands spacedapart from each other by about 94 GHz. Each of these sidebands isdirected to distinct generator outputs by the optical filter 30 and canbe selectively combined by the switching circuitry 130 to yieldcontinuous-wave optical modulation in the W-band, i.e., at 94 GHz.

Accordingly, as is illustrated in FIG. 2D, the signal generator andswitching circuitry of this aspect of the present invention can beoperatively coupled to a programmable controller or other suitablecontrol hardware to provide an effective means of controlling themodulation frequency of the electrooptic source 10 over a wide range.The source 10 may be scanned through a plurality of modulation bands oracross a broad frequency range in a substantially continuous manner bycontrolling the drive frequency and selecting/combining suitablesidebands to yield a desired modulation frequency. It is contemplatedthat a frequency-scanned optical output or different combinations ofdistinct-frequency optical outputs can be directed to a commonoptical/electrical converter 140, a plurality of differentoptical/electrical converters 140, or both. It is further contemplatedthat modulated optical signals can be directed to a singleoptical/electrical converter 140 at a single portal 170, to a pluralityof optical/electrical converters in a single portal, or to a pluralityof optical/electrical converters 140 distributed across several portals170. The optical circuitry 130 can be configured to do so by splittingthe modulated optical signal into a plurality of modulated outputs, byredirecting the modulated optical signal sequentially from oneoptical/electrical converter 140 to the next, or both.

The optical circuitry 130 can also be configured to encode the modulatedoptical signal prior to direction to an optical/electrical converter140. For example, once the modulated optical signal has beenestablished, a tone or digital signature can be incorporated on theoptical carrier by utilizing, for example, the data encoder described indetail below with reference to FIGS. 2A, 2B and 7. Since it is generallyeasier to modulate an optical signal than to modulate a THz signal, thetone or digital signature is encoded onto the signal in the opticaldomain. A relatively simple modulator configured as a Mach-Zehnderinterferometer can be used to encode the tone or digital signature. Itis contemplated that alternative means may be employed to modulate theoptical signal in the optical or electrical domain without departingfrom the scope of the present invention.

Once the tone or digital signature is encoded onto the modulated opticalsignal, the composite signal can optionally be amplified. The opticalamplification is relatively straight forward. Optical amplifiers, suchas Erbium-doped fiber amplifiers will increase optical power withoutexcessive loss of data modulation on the optical signal. After thepotential amplification, the optical signal then is switched or split,to send the signal to the various mmw emitters at the various mmwsecurity portals. Optionally, amplification of the optical signal canoccur after the switching or splitting of the optical signal.

Although the detectors 150 may take a variety of conventional or yet tobe developed forms suitable for converting the reflected mmw signals tosignals representing the attenuation of the millimeter or sub-millimeterwave 100 upon reflection from the object 200, according to oneembodiment of the present invention, the detector 150 comprises anantenna assembly comprising a tapered slot antenna portion 20′ and anelectrooptic waveguide portion 30′, the structure of which is describedin detail below with reference to FIGS. 12-19.

Referring collectively to FIGS. 2-11 and initially to FIG. 2A, anelectrooptic source 10 suitable for use in security portals according tosome embodiments of the present invention is illustrated. Generally, theillustrated electrooptic source 10 comprises, among other things, asideband generator 20, an optical filter 30, and a waveguide network 55configured to direct an optical signal from an optical input 12 of theelectrooptic source 10 through the sideband generator 20 and the opticalfilter 30 to an optical output 14 of the electrooptic source 10. As willbe discussed in greater detail with reference to FIGS. 3-5 below, thesideband generator 20 is configured to generate frequency sidebands Sabout a carrier frequency λ₀ of the input optical signal I_(IN). Theoptical filter 30 is configured to discriminate between the frequencysidebands S and the carrier frequency λ₀ so as to direct particularsidebands of interest to the optical output 14 in the form of amillimeter wave optical signal I_(MMW). Where data-encoded modulation ofthe output signal is desired, the electrooptic source 10 furthercomprises a data encoder 40 configured generate an encoded optical datasignal I_(D).

The sideband generator 20 can be configured as an electroopticinterferometer. More specifically as a Mach-Zehnder interferometer wherean optical signals propagating in the input segment of theinterferometer is divided into two equal parts at, e.g., a Y-splitter.The two optical signals propagate down the two arms of theinterferometer before being recombined with, e.g., a Y-combiner. If thetwo optical signals are in phase at the Y-combiner, the signalsconstructively interfere and the full intensity propagates out theoutput waveguide. If, however, the two optical signals are out of phase,then the signals destructively interfere and the output intensity isreduced. If the signals at the Y-combiner are out of phase by π radians,then the two signals will destructively interfere and the output will beat a minimum.

For an electrooptically-controlled Mach-Zehnder interferometer, forexample, a 12 GHz voltage applied to the electrooptic waveguides via, amodulation signal input terminal 22 and a 50Ω control signal termination24, will induce a phase shift that will adjust the constructive anddestructive interference at the signal combiner. When the voltageapplied to the electrooptic waveguides induces a π phase shift betweenthe two arms, the output will be minimized. The voltage that induces theπ phase is known as Vπ. By way of illustration and not limitation,specific teachings on some suitable control electrode and waveguideconfigurations for use in the sideband generator 20 and data encoder 40of the present invention are presented in U.S. PG Pub. Nos. 2005/0226547A1 for Electrooptic Modulator Employing DC Coupled Electrodes and2004/0184694 A1 for Electrooptic Modulators and Waveguide DevicesIncorporating the Same.

When the electrooptic interferometer is biased at −π/2 and is modulatedat a frequency of f_(m) (note: ωm=2πf_(m)), then the magnitude of theoutput optical signal at the fundamental frequency and at each of theodd harmonics (i.e. 3ω_(m), 5ω_(m), . . . ) can be calculated usingBessel functions. Table 1 summarizes the magnitude of the fundamentaland odd harmonics.

Peak-to-Peak Amplitude of Harmonic Drive Voltage (V_(m)) Voltage ω_(m) 3ω_(m) 5 ω_(m) 7 ω_(m) V_(π)/4 V_(π)/2 0.363 0.009 7.5e−5 2.8e−7 V_(π)/2V_(π) 0.567 0.069 0.0022 3.4e−5 V_(π) 2 V_(π) 0.285 0.333 0.052 0.003 2V_(π) 4 V_(π) −0.212 0.029 0.373 0.157

From Table 1, we can see that if the modulator is driven with a voltageless than V_(π), then the amplitude of the harmonics is quite low.However, as the modulator gets driven harder, the magnitude of theharmonics becomes larger than the fundamental. FIGS. 3A-3D show thetime-domain response of the interferometer with drive voltage amplitudesequal to V_(π)/4, V_(π)/2, V_(π), and 2V_(π). The odd harmonic 3ω_(m)dominates the carrier frequency ω_(m) in FIG. 3C. In FIG. 3D, the oddharmonic 5ω_(m) dominates the carrier frequency ω_(m).

FIG. 4 graphically shows the relationship between the amplitude of thefundamental, third, fifth, and seventh harmonics and the normalizeddrive voltage, V_(m)/V_(π). As can be seen from FIG. 4, if theelectrooptic modulator functioning as the sideband generator 20 isdriven with a voltage amplitude a little larger than 2V_(π), then theamplitude of the fifth harmonic (W5) will be maximum. Regardless ofwhich sideband is selected as the sideband of interest, it iscontemplated that the control signal can be selected such that itapproximates a sinusoidal voltage where the amplitude of the sideband ofinterest reaches a maximum.

Referring to FIGS. 5A-5C, given the example where a 1550 nm opticalsignal is modulated at 10 GHz, the fundamental modulation frequency andany harmonics will be present as sidebands on the optical carrier at+/−0.08 nm from the 1550 nm carrier. FIG. 5A shows an unmodulatedoptical signal. FIG. 5B shows the optical spectrum at the output of thesideband generator 20 with V_(m)=Vπ. FIG. 5C shows the spectrum withV_(m)=2Vπ. The optical spectrum in FIG. 5C shows dominant sidebands at1549.52 nm and 1550.48 nm. In the frequency domain, these wavelengthscorrespond to 193,608.4 GHz and 193,488.4 GHz, respectively. Thedifference between these two frequencies is 120 GHz. Again, thiscorresponds to +/− the fifth harmonic of the 12 GHz modulation frequency(i.e. +/−5*12 GHz or +/−60 GHz).

It is contemplated that the sidebands of interest need not dominate theoptical signal output from the sideband generator 20. Rather, in manyembodiments of the present invention, it may be sufficient to merelyensure that the magnitude of the frequency sidebands of interest, at anoutput of the sideband generator, is at least about 10% of a magnitudeof the optical carrier signal at the optical input of the electroopticsource.

Regarding the optical filter 30, as is noted above, the purpose of theoptical filter 30 is to select the desired sidebands and remove thecarrier frequency and any unwanted sidebands. This optical filteringfunction can be accomplished using a variety of technologies, includingBragg grating reflective filters, wavelength-selective Mach-Zehnderfilters, multilayer thin film optical filters, arrayed waveguidegratings (AWG), micro ring resonator filters, and directional couplerfilters that are wavelength selective. An arrayed waveguide grating isparticularly useful because it is an integrated optical device withmultiple channels characterized by very narrow bandwidths. The followingdiscussion focuses on the use of an AWG, although other filters can alsobe used in accordance with the present invention.

The role of the AWG is to filter out the undesirable sidebands and, withthe cooperation of a signal combiner, combine the two sidebands ofinterest. For example, an AWG with a channel spacing of 60 GHz (Δλ=0.48nm) or a channel spacing of 30 GHz (Δλ=0.24 nm) would be well-suited forthe 120 GHz system described above. As is illustrated schematically inFIG. 6, where sideband wavelengths generated from the sideband generatoras a modulated optical signal I_(MOD) are fed into the optical filter30, each of the sidebands will come out a separate output channel of thefilter 30 according to its characteristic wavelength. By way ofillustration, not limitation, if the output of the sideband generator 20is inserted into the AWG, then the two desired 5^(th) order harmonicswould come out of ports 3 and 7, as shown schematically in FIG. 6. If,however, a 60 GHz AWG is used, the desired 5^(th) order sidebands wouldcome out less displaced but still distinct ports, i.e., ports 4 and 6.One advantage of the 30 GHz AWG is that the port bandwidths are muchnarrower. However, 30 GHz AWGs are often more difficult to produce andoperate. For these reasons, it may be preferable to operate someembodiments of the present invention by utilizing a 60 GHz AWG as theoptical filter 30.

A signal combiner 70 according to the present invention is alsoillustrated in FIG. 6, where the desired sidebands are combined with awaveguide Y-combiner. For example, if two fifth harmonic sidebands arecombined at the signal combiner 70, the optical signal I_(MMW) will havea continuous-wave modulation of 120 GHz. It is contemplated that asignal combiner would not be necessary where the optical filtercomprises an optical device that is configured to maintain propagationof the sidebands of interest along a unitary optical path.

Referring to FIG. 7, once the modulated optical signal I_(MMW) isformed, data can be incorporated on the carrier by utilizing, forexample, a 10 GB/s electrical data signal coupled to the data encoder 40via the data signal input terminal 42 and the 50Ω control signaltermination 44. Since it is generally easier to modulate an opticalsignal than to modulate a THz signal, data is encoded onto the signalI_(MMW) in the optical domain. Here a simple modulator configured as aMach-Zehnder interferometer is used to encode the data. It iscontemplated that alternative means may be employed to modulate theoptical signal I_(MMW) in the optical or electrical domain withoutdeparting from the scope of the present invention.

Once the data is encoded onto the modulated optical signal, thecomposite signal I_(D) can be amplified and then converted to the THzportion of the spectrum. The optical amplification is relativelystraight forward. Optical amplifiers, such as Erbium-doped fiberamplifiers will increase optical power without excessive loss of datamodulation on the optical signal.

By way of illustration and not limitation, in one mode of operation, astandard telecommunications-grade laser diode 15 operating in thecontinuous-wave (CW) mode at a bandwidth centered at about 1550 nmprovides the optical carrier frequency λ₀ used in the optical portion ofthe device 10. An electrooptic modulator functions as the sidebandgenerator 20 and is overdriven in the manner described below such thatthe resulting optical signal includes a plurality of sidebands S on theoptical carrier λ₀. For example, an appropriately configured modulatoroverdriven at twice Vπ, where Vπ represents the voltage at which a πphase shift is induced between respective arms of the modulator, willgenerate sidebands of interest at 5 times the modulation frequency.Accordingly, overdriving the modulator at 12 GHz will generate sidebandsof interest about the 1550 nm optical carrier at +/−60 GHz.

A telecommunications-grade arrayed waveguide grating (AWG) with 60 GHzchannels can be used as the optical filter 30 to filter out the carrieroptical signal λ₀ and combine the two optical sidebands of interest,forming the millimeter wave optical signal modulated at 120 GHz. Asecond electrooptic modulator is used as the data encoder 40 to encodedata onto the mmw-modulated optical signal and generate a data-encodedsignal I_(D). A telecommunications grade optical modulator using theelectrooptic effect to control the phase in a Mach-Zehnderinterferometer can encode data at 10 GB/s or higher.

An optical amplifier 75 increases the modulated optical signal I_(D)prior to conversion in a suitable optical/electrical converter 80. Theoptical/electrical converter 80 can take a suitable conventional or yetto be developed form. For example, and not by way of limitation, a highspeed photodiode, tuned to operate at 0.12 THz can be used to remove theoptical carrier and convert the signal I_(D) to a modulated THz signalE_(D).

Although many embodiments of the present invention are illustratedherein with reference to optical signal splitters and combiners in theform of directional coupling regions, it is noted that the presentinvention contemplates utilization of any suitable conventional or yetto be developed structure for optical signal splitting or combining. Forexample, suitable alternative structures for splitting and combiningoptical signals include, but are not limited to, 2×2 directionalcoupling regions, 1×2 directional coupling regions, 1×2 Y signalsplitters and combiners, and 1×2 and 2×2 multimode interference elementsplitters and combiners. The specific design parameters of thesestructures are beyond the scope of the present invention and may begleaned from existing or yet to be developed sources, including U.S.Pat. No. 6,853,758, issued Feb. 8, 2005, the disclosure of which isincorporated herein by reference.

Up to this point, the present discussion has assumed that the initialMach-Zehnder was biased with a phase difference in the two arms ofV_(π)/2. However, if the modulator is biased so that the phasedifference is equal to π (or a multiple of π), then the output opticalsignal will have even harmonics (2ω, 4ω, 6ω, . . . ) of the modulationsignal. If the sideband generator 20 is driven with a voltage less thanV_(π), then the amplitude of the harmonics will be relatively low.However, as the sideband generator 20 gets driven harder, the magnitudeof the harmonics becomes larger than the fundamental carrier frequency.FIGS. 8A-8D show the time-domain response of the sideband generator 20with drive voltage amplitudes equal to Vπ/4, V_(π)/2, V_(π), and 2V_(π).It should be noted that for this bias configuration, there is nomodulation at the fundamental frequency. Instead, the 2^(nd) harmonicbegins to grow immediately.

FIG. 9 is a graphic representation of the amplitude of the evenharmonics, as a function of drive voltage. The graph shows the amplitudeof the second harmonic (W2), the fourth harmonic (W4), and the sixthharmonic (W6). The data for J0 corresponds to a relative optical bias ofthe optical signal. Using the analysis developed earlier, this π biasconfiguration could be used to form sidebands at two four, and six timesthe modulation frequency. If we assume a drive frequency of 12 GHz, thisbias method could be used to produce optical signals with CW-modulationat 96 GHz (+/− the fourth harmonic) and 144 GHz (+/− the sixthharmonic).

It is contemplated that the drive frequency need not be fixed at aparticular value. Specifically, if the 12 GHz modulation control signalis instead provided as a variable frequency source, the frequency of theTHz-band signal can also be variable. For example, if the 12 GHz controlsignal is changed to 12.5 GHz, then the difference of the fifthharmonics will change form 120 GHz to 125 GHz. Of course, any change inthe frequency of the harmonics may necessitate a change in theoperational parameters of the filter 30 because the new sidebands ofinterest will need to make it through the filter 30. In a similar way,adding optical switches between the optical filters and the Y-combinerwill allow various sidebands to be combined. This can provideflexibility in obtaining a range of continuous wave modulated opticalsignals.

Referring to FIG. 10, it is further contemplated that the sidebandgenerator 20 may take the form of a phase modulator, as opposed to theinterferometer described above with reference to FIGS. 1-9. FIG. 10 is aschematic illustration of a suitable phase modulator configurationaccording to this aspect of the present invention. Generally, the phasemodulator sideband generator 20 consists of a straight waveguide 52 withan electrooptic core and/or cladding configured such that, when anelectric field is applied across an electrooptically functional portion56 of the sideband generator 20, the refractive index in the waveguide52 will change, which in turn will advance or retard the phase of theoptical signal propagating through the functional portion 56 of thewaveguide 52.

The signal output of a phase modulator of the type illustrated in FIG.10 can be represented by:

$E_{out} = {E_{i\; n}{\cos \left( {{\omega_{c}t} + {\frac{v_{m}\pi}{v_{\pi}}{\sin \left( {\omega_{m}t} \right)}}} \right)}}$

where ω_(c) is the optical frequency, ω_(m) is the modulation frequency,and the electric field and intensity of the signal can be represented as

I=E²

If the magnitude of the phase modulator voltage is such thatv_(m)=v_(π), then the phase term will modulate between +π and −π as sinω_(m)t varies from −1 to 1. Stated differently, under the conditionv_(m)=v_(π), we will have a 2π phase shift.

As we note above in the context of the interferometer-based sidebandgenerator, the magnitude of the output optical signal at the fundamentalfrequency and at each of the odd harmonics (i.e. 3ω_(m), 5ω_(m), . . . )can be calculated using Bessel functions. FIGS. 11A-11D illustrate therelative magnitudes of the fundamental and odd harmonics at the outputof a phase modulator sideband generator 20 according to the presentinvention with V_(m)=0.01Vπ, V_(m)=0.50Vπ, V_(m)=Vπ, and V_(m)=2.04Vπ.As is the case for the interferometer-based sideband generator 20, themagnitude of the fifth-order harmonic for the phase modulator sidebandgenerator 20 reaches a maximum at V_(m)=2.04Vπ.

A number of factors come into play when choosing between aninterferometer-based sideband generator 20 and a phase modulatorsideband generator 20. Specifically, in the case of the interferometerthe output intensity varies with drive voltage and the DC bias on theinterferometer can be used to adjust the output intensity signal andcontrol the relative height of the sidebands. In contrast, when thesideband generator 20 is configured as a phase modulator, the outputintensity remains relatively constant as the drive voltage isvaried—only the phase of the optical signal is varied. In addition, theDC bias if the drive voltage will not affect output intensity and willnot alter the height of the sidebands generated by the phase modulator.A phase modulator is as efficient at generating sidebands as aninterferometer. For example, referring to FIGS. 4 and 11D, both types ofsideband generators will optimize the 5th harmonic with a drive signalof about 2.04Vπ.

Interferometers can be run in a push-pull configuration and cantherefore obtain a π phase shift in half the length of a singlewaveguide device. Phase modulators cannot be run in a push-pullcondition. Accordingly, with equivalent electrooptic material, a phasemodulator would have to be roughly twice as long as an interferometer.However, if an interferometer is biased at π/2, it will have a 3 dB(50%) inherent loss. In contrast, the phase modulator is not subject tothis inherent loss. Accordingly, those practicing the present inventionmay wish to consider these factors and the optical attenuation ofavailable electrooptic materials in choosing betweeninterferometer-based and phase modulator type sideband generators.

As is illustrated schematically in FIG. 2B, the sideband generator 20,the optical filter 30, the data encoder 40, and the waveguide network55, are configured such that they can be conveniently formed over acommon device substrate 60. Specifically, as will be appreciated bythose familiar with the optical waveguides, electrooptic modulators, andarrayed waveguide gratings described in the literature and in the U.S.patent documents incorporated by reference below, the respectivefunctional structures of the sideband generator 20, the optical filter30, the data encoder 40, and the waveguide network 55 are each suitablefor fabrication over a common substrate 60 comprising, for example, asilica cladding layer supported by a silicon underlayer. This ability tobe formed over a common device substrate holds true even where therespective structures of these devices incorporate diverse componentsand configurations. Accordingly, it is noted that the scope of thepresent invention extends to general device configurations and is notlimited to the provision of a sideband generator 20 that is driven at acontrol voltage that is larger than Vπ.

The embodiment illustrated in FIG. 2B may also include a waveguidenetwork 50 that comprises a substantially continuous waveguide coreextending from the optical input 12 of the device 10 to the opticaloutput 14 of the device 10. More specifically, referring to FIG. 2B infurther detail, the waveguide network 50 may comprise operationalwaveguide portions 52 and transitional waveguide portions 54. Theoperational waveguide portions would be defined in the sidebandgenerator 20, the optical filter 30, and the data encoder 40 while thetransitional waveguide portions 54 would be configured to direct anoptical signal between the optical input 12, the sideband generator 20,the optical filter 30, the data encoder 40, and the optical output 14 ofthe electrooptic source 10. Given these portions it is contemplated thatthe operational and the transitional waveguide portions 52, 54 can becomprised of a common optical transmission medium that is present overat least a majority of the respective optical path lengths defined bythe operational and transitional waveguide portions 52, 54. Further, theoperational and transitional waveguide portions 52, 54 can be configuredto define a substantially planar lightwave circuit.

The waveguide medium of the waveguide network may comprise asilica-based waveguide formed over a silica cladding layer while thewaveguide medium of the sideband generator may comprise a waveguide coresurrounded by or embedded within a polymeric electrooptic claddingmedium. Nevertheless, the distinct components lend themselves toformation over a common substrate, often in the nature of a planarlightwave circuit (PLC). For the purposes of defining and describing thepresent invention, it is noted that the term “over” contemplates thepresence of intervening layers between two layers or regions. Forexample, a waveguide medium formed over a silicon substrate contemplatesthe possibility of intervening layers between the waveguide medium andthe silicon substrate. The specific composition of the opticaltransmission medium forming the waveguide core is not a point ofemphasis in many embodiments of the present invention and may, forexample, be selected from materials comprising doped or undoped silica,doped or un-doped silicon, silicon-oxynitride, polymers, andcombinations thereof.

For the purposes of describing and defining the present invention, it isnoted that a planar lightwave circuit (PLC) typically merely defines anoptical input, an optical output, and points of propagation therebetween that lie in a substantially common plane or are formed over asubstantially planar circuit component. Use of the word “circuit” hereinis not intended to create an inference that an optical signalpropagating in a PLC returns to its point of origin.

A variety of configurations may be utilized to form the electroopticmodulators of the present invention. For example, and not by way oflimitation, the functional regions of the electrooptic modulators maycomprise: electrooptically clad silica waveguides; silicon waveguideswith electroabsorptive modulators where charge injected into the siliconwaveguide makes the waveguide opaque; sol-gel waveguides withelectrooptic claddings; lithium niobate waveguides, where the refractiveindex of the waveguide is dependent upon an applied electric field; andelectrooptic polymer waveguides. For example, and not by way oflimitation, where the electrooptic modulator comprises a waveguide coreand an optically functional cladding region optically coupled to thewaveguide core, the optically functional cladding region may comprise apoled or un-poled electrooptic polymer dominated by the Pockels Effect,the Kerr Effect, or some other electrooptic effect.

For the purposes of describing and defining the present invention, it isnoted that an electrooptic functional region is a region of an opticalwaveguide structure where application of an electrical control signal tothe region alters the characteristics of an optical signal propagatingalong an optical axis defined in the waveguide structure to asignificantly greater extent than in non-electrooptic regions of thestructure. For example, electrooptic functional regions according to thepresent invention may comprise an electrooptic polymer configured todefine an index of refraction that varies under application of asuitable electric field generated by control electrodes. Such a polymermay comprise a poled or un-poled electrooptic polymer dominated by thePockels Effect, the Kerr Effect, or some other electrooptic effect.These effects and the various structures and materials suitable fortheir creation and use are described in detail in the context ofwaveguide devices in the following published and issued patentdocuments, the disclosures of which are incorporated herein byreference: U.S. Pat. Nos. 6,931,164 for Waveguide Devices IncorporatingKerr-Based and Other Similar Optically Functional Mediums, 6,610,219 forFunctional Materials for use in Optical Systems, 6,687,425 forWaveguides and Devices Incorporating Optically Functional CladdingRegions, and 6,853,758 for Scheme for Controlling Polarization inWaveguides; and U.S. PG Pub. Nos. 2005/0226547 A1 for ElectroopticModulator Employing DC Coupled Electrodes, 2004/0184694 A1 forElectrooptic Modulators and Waveguide Devices Incorporating the Same,and 2004/0131303 A1 for Embedded Electrode Integrated Optical Devicesand Methods of Fabrication. Further, it is noted that, various teachingsregarding materials and structures suitable for generating the PockelsEffect, the Kerr Effect, and other electrooptic effects in an opticalwaveguide structure are represented in the patent literature as a whole,particularly those patent documents in the waveguide art assigned toOptimer Photonics Inc. or naming Richard W. Ridgway, Steven M. Risser;Vincent McGinniss, and/or David W. Nippa as inventors.

For the purposes of defining and describing the present invention, it isnoted that the wavelength of “light” or an “optical signal” is notlimited to any particular wavelength or portion of the electromagneticspectrum. Rather, “light” and “optical signals,” which terms are usedinterchangeably throughout the present specification and are notintended to cover distinct sets of subject matter, are defined herein tocover any wavelength of electromagnetic radiation capable of propagatingin an optical waveguide. For example, light or optical signals in thevisible and infrared portions of the electromagnetic spectrum are bothcapable of propagating in an optical waveguide. An optical waveguide maycomprise any suitable signal propagating structure. Examples of opticalwaveguides include, but are not limited to, optical fibers, slabwaveguides, and thin-films used, for example, in integrated opticalcircuits.

For the purposes of defining and describing the present invention, it isnoted that a Mach-Zehnder interferometer structure generally comprisesan optical configuration where an optical signal propagating along awaveguide is split into a pair of waveguide arms and recombined into asingle waveguide following treatment of the respective optical signalspropagating in one or both of the waveguide arms. For example, thesignal in one of the waveguide arms may be treated such that the opticalsignal propagating therein is subject to a given phase delay. As aresult, when the signals of the respective waveguide arms arerecombined, they interfere and generate an output signal indicative ofthe interference. A number of Mach-Zehnder interferometer structures areillustrated in detail in the above-noted patent documents.

The detectors 150 illustrated schematically in FIG. 1 may take any formsuitable for the detection and analysis of millimeter and submillimeterwaves. For example, and not by way of limitation, the detectors 150 maycomprise Schottky diode detectors, examples of which include: a GaAsbeamlead detector diode, which may be fabricated using the modifiedbarrier integrated diode (MBID) process described in U.S. Pat. No.4,839,709; and silicon zero bias Schottky detectors, which exhibit goodperformance at room temperature and frequencies under 10 GHz.

Referring collectively to FIGS. 12-19, according to one embodiment ofthe present invention, the detectors 150 can be configured as anelectrooptic antenna assembly 150. Generally, the antenna assembly 150comprises an antenna portion 20′ and an electrooptic waveguide portion30′. The antenna portion 20′ is configured as a tapered slot antenna,the design of which will be described in further detail below withreference to FIGS. 14 and 15. The waveguide portion 30′ comprises atleast one electrooptic waveguide 32′ that extends along at least aportion of an optical path between an optical input 34′ and an opticaloutput 36′ of the antenna assembly 150.

The electrooptic waveguide 32′ comprises a waveguide core 35′ thatextends substantially parallel to a slotline 22′ of the tapered slotantenna 20′ in an active region 15′ of the antenna assembly 150 and atleast partially comprises a velocity matching electrooptic polymer 38′in the active region 15′ of the antenna assembly 150. It is contemplatedthat the velocity matching electrooptic polymer 38′ may form thewaveguide core 35′, all or part of the cladding surrounding anon-polymeric waveguide core, or both the core 35′ and the cladding ofthe waveguide 32′.

The tapered slot antenna 20′ and the electrooptic waveguide 32′ arepositioned relative to each other such that: (i) the velocity v_(e) of amillimeter or sub-millimeter wave signal 100 traveling along the taperedslot antenna 20′ in the active region 15′ is at least partially afunction of the dielectric constant of the velocity matchingelectrooptic polymer 38′ and (ii) the velocity v_(O) of an opticalsignal propagating along the waveguide core 35′ in the active region 15′is at least partially a function of the index of refraction of thevelocity matching electrooptic polymer 38′. For the purposes ofdescribing and defining the present invention, it is noted thatreference herein to a variable being a “function” of a parameter oranother variable is not intended to denote that the variable isexclusively a function of the listed parameter or variable. Rather,reference herein to a variable that is a “function” of a listedparameter is intended to be open ended such that the variable may be afunction of a single parameter or a plurality of parameters.

Given this common dependency on the properties of the velocity matchingelectrooptic polymer 38′, the active region 15′ and the velocitymatching electrooptic polymer 38′ of the antenna assembly 150 can beconfigured to enhance the velocity matching of the millimeter wave andthe optical signal in the active region 15′. For example, It iscontemplated that the active region 15′ and the velocity matchingelectrooptic polymer 38′ can be configured such that v_(e) and v_(O) aresubstantially the same in the active region or such that they at leastsatisfy the following relation:

$\frac{{v_{e} - v_{O}}}{v_{O}} \leq {20{\%.}}$

Although the antenna assembly described above is not limited to specificantenna applications, the significance of the velocity matchingcharacteristics of the assembly can be described with reference toapplications where a millimeter-wave signal traveling along the taperedslot antenna 20′ creates sidebands on an optical carrier signalpropagating in the waveguide core 35′. Specifically, as is describedabove with reference to FIGS. 2-11, a millimeter-wave signal can be usedto create sidebands on an optical carrier by directing a coherentoptical signal of frequency ω_(0′) along the electrooptic waveguideportion of an electrooptic modulator while a millimeter-wave voltage offrequency ω_(m) is input to the traveling wave electrodes of themodulator. In the embodiment of the present invention illustrated inFIGS. 12 and 13, the first and second electrically conductive elements24′, 26′ of the tapered slot antenna 20′ and the electrooptic waveguide32′ form the electrooptic modulator and a coherent optical carriersignal is directed along the electrooptic waveguide 32′. The first andsecond electrically conductive elements 24′, 26′ function in a mannerthat is analogous to the respective traveling wave electrodes describedin the aforementioned publication and, as such, cooperate with theelectrooptic waveguide 32′ to create sidebands on the optical carrierpropagating along electrooptic waveguide 32′.

More specifically, as the optical carrier ω_(0′) and millimeter-wavesignal 100 co-propagate along the length of the electrooptic modulatorformed by the tapered slot antenna 20′ and the electrooptic waveguide32′, the interaction of the electric field of the millimeter-wave 100with the electrooptic material of the polymer in the active region 15′creates a refractive index change in the electrooptic waveguide 32′which oscillates with the time-varying electric field of themillimeter-wave 100. This time variation of the refractive index resultsin a time-dependent phase shift of the optical carrier, which isequivalent to imparting sidebands to the optical carrier ω₀. Themodulation of the optical carrier by the millimeter-wave voltage resultsin an optical output from the modulator which has a component at thecarrier frequency ω_(0′) and at sideband frequencies ω₀±ω_(m). Thepresent inventors have recognized that magnitude of the response at thesidebands is determined by the ratio of the millimeter-wave voltage toV_(π), the voltage required to completely change the modulator from theon to the off state, and by the degree of velocity matching between theoptical carrier and the millimeter-wave that co-propagate along themodulator.

Although the millimeter-wave voltage is an external variable, the degreeof velocity matching between the optical carrier and the millimeter-waveis primarily a function of the design parameters of the antenna assembly150 and, as such, can be optimized through careful control of the designof the parameters of the antenna assembly 150. For example, as themillimeter-wave propagates through the active region 15′, whichcomprises the electrically conductive elements 24′, 26′ of the taperedslot antenna 20′ and a dielectric substrate 40′, the velocity v_(e) ofthe millimeter or sub-millimeter wave signal in the active region 15′ isa function of effective permittivity ∈_(eff) of the active region 15′:

$v_{e} = {c/\sqrt{ɛ_{eff}}}$

In the active region 15′, the dielectric substrate 40′ defines athickness t and comprises a base layer 42′, the waveguide core 35′, thevelocity matching electrooptic polymer 38′, at least one additionaloptical cladding layer 44′, each of which contribute to the thickness tin the active region 15′. Thus, the effective permittivity ∈_(eff) ofthe active region 15′ is a function of the substrate thickness t and therespective dielectric constants of the base layer 42′, the waveguidecore 35′, the velocity matching electrooptic polymer 38′, and theadditional optical cladding layers 44′.

The velocity v_(O) of the optical signal propagating along the waveguide32′ in the active region 15′ is a function of the effective index ofrefraction η_(eff) of the active region 15′:

v_(O) = c/η_(eff)

The effective index of refraction η_(eff) of the active region 15′ is afunction of the respective indices of refraction of the waveguide core35′, the velocity matching electrooptic polymer 38′, and the additionaloptical cladding layers 44′. Accordingly, the degree of velocitymatching between the optical carrier and the millimeter-wave can beoptimized by controlling the effective permittivity ∈_(eff) and theeffective index of refraction η_(eff) of the active region 15′.

Where a velocity matching electrooptic polymer is selected as acomponent of the waveguide 32′, it is possible to configure theelectrooptic modulator such that the effective index of refractionη_(eff) of the active region 15′ is 1.5 and the velocity v_(O) of theoptical signal is:

v_(O) = c/1.5

In the same context, if we select a silica-based dielectric substrate40′ and use the velocity matching electrooptic polymer in the waveguide32′, it is possible to configure the active region such that theeffective permittivity ∈_(eff) of the active region is 2.25 and thevelocity v_(e) of the millimeter or sub-millimeter wave signal matchesthe velocity v_(O) of the optical signal:

$v_{e} = {{c/\sqrt{2.25}} = {c/1.5}}$

In contrast, the velocity v_(e) of the millimeter or sub-millimeter wavesignal in a conventional silica-based tapered slot antenna having aneffective permittivity ∈_(eff) of about 3.76 would be significantlydifferent than the velocity v_(O) of the optical signal:

$v_{e} = {{c/\sqrt{3.76}} = {c/1.94}}$

To maintain total phase shift in the electrooptic modulator structure ofthe active region 15′ within 50% of the maximum possible phase shift,the active region 15′ and the velocity matching electrooptic polymer 38′should be configured such that the velocity v_(e) and the velocity v_(O)satisfy the following relation:

${{1 - \frac{v_{e}}{v_{O}}}} \leq \frac{2.8}{L\; \beta}$

where L is the length of the active region and β is the propagationconstant of the waveguide.

One method to achieve velocity matching is to use materials where therespective velocities of the optical signal and the millimeter-wave areeffectively equal. Velocity matching can also be achieved throughspecialized device design. For example, the thickness of the dielectricsubstrate or any of its component layers can be tailored through siliconmicromachining, reactive ion etching, or otherwise to achieve velocitymatching. Alternatively, one can construct an effective dielectricconstant by altering the geometry of the dielectric substrate 40′, e.g.,by forming holes in the dielectric, or changing the shape or dimensionsof the dielectric. Referring to the antennae 20′ illustrated in FIGS. 14and 15, in the context of a 94 GHz wave traveling along the antennae20′, assuming the slotline 22′ is characterized by an electrode gap of20′ microns in the active region 15′ and the electrodes 24′, 26′ arefabricated on silica, a dielectric substrate thickness t ofapproximately 170 microns can form the basis of a device design withsuitable velocity matching between the millimeter wave and an opticalsignal wave.

The antenna assembly 150 illustrated in FIGS. 12 and 13 is configuredsuch that an optical signal propagating from the optical input 34′ tothe optical output 36′ merely passes through a single active region 15′comprising a single tapered slot antenna 20′. Turning more specificallyto the design of the tapered slot antenna 20′, it is noted that taperedslot antennae (TSA) are end-fire traveling wave antennae and typicallyconsist of a tapered slot etched onto a thin film of metal. This can bedone either with or without a dielectric substrate on one side of thefilm. Planar tapered slot antennae have two common features: theradiating slot and a feed line. The radiating slot acts as the groundplane for the antenna and the antenna is fed by the feed line, whichmay, for example, be a balanced slotline or any suitable feed structure.The nature of the specific feed structure to be used is beyond the scopeof the present invention and may be gleaned from any conventional or yetto be developed teachings on the subject, including those teachings setforth in U.S. Pat. No. 6,317,094, the germane portions of which areincorporated herein by reference. Generally, the feed structure shouldbe relatively compact and have low loss. Suitable feed structuresinclude, but are not limited to, coaxial line feeds and the microstripline feeds. For the purposes of defining and describing the presentinvention, it is noted that reference herein to an antenna “assembly” isnot intended to imply that the assembly is a one-piece, integralassembly or even an assembly where all of the recited components arephysical connected to each other. Rather, antenna assemblies accordingto the present invention may merely be a collection of components thatare functionally linked to each other in a particular manner.

Many taper profiles exist for TSA including, but not limited to,exponential, tangential, parabolic, linear, linear-constant,exponential-constant, step-constant, broken linear, etc. FIG. 14 shows alinearly tapered profile. FIG. 15 shows a Vivaldi profile. In FIGS. 14and 15, the gap between the first and second electrically conductiveelements 24′, 26′ of the tapered slot antenna 20′ is much smaller in theactive region 15′, e.g., on the order of 20′ microns, and behaves muchmore like a waveguide for the millimeter-wave signal. The reduction inthe gap between the two electrically conductive elements 24′, 26′ of theantenna 20′ increases the magnitude of the electric field of themillimeter-wave signal, which is important for electrooptic materialswhere the response is proportional to the electric field, as opposed tothe voltage across the gap. In operation, incident millimeter-waveradiation enters the antenna opening and propagates along the antennaelements 24′, 26′ toward the active region 15′. The millimeter-wavesignal exits the active region 15′ and can be re-radiated or terminatedinto a fixed impedance.

The antenna assemblies illustrated in FIGS. 12-15 may, for example, befabricated by first providing the base layer 42′ with a degree ofsurface roughness that is sufficiently low for optical applications. Thelower cladding 44′ is coated onto this substrate and a waveguide patternis etched therein. The waveguide core and the velocity matchingelectrooptic polymer 38′, which may be formed of the same or differentmaterials, are then coated onto the etched cladding and an uppercladding 44′ is formed over the electrooptic layer 38. Finally, theelectrically conductive elements 24′, 26′ of the tapered slot antenna20′ are fabricated on the top cladding.

The electrooptic material 38′ can be poled, if required for theresponse. The refractive indices of the lower and upper claddings 44′are lower than that of the electrooptic layer 38′, and the thickness ofthe claddings 44′ are sufficient to optically isolate the opticalcarrier from the substrate 42′ and the antenna 20′. The thickness of theelectrooptic layer 38′ is such that guided modes of the optical carrierare confined to the defined electrooptic waveguide. Although waveguidefabrication has been described herein in the context of etching thelower cladding, any other method for forming an electrooptic waveguidein an electrooptic material, such as etching the electrooptic material,photobleaching, or diffusion, can be used to define the electroopticwaveguide.

As is noted above, the tapered slot antenna 20′ comprises first andsecond electrically conductive elements 24′, 26′ arranged to define theradiating slot of the antenna 20′. Although the embodiments of FIGS.12-15 include first and second electrically conductive elements 24′, 26′arranged in a common plane, above the electrooptic waveguide 32′,alternative configurations are contemplated. For example, referring toFIGS. 16 and 17, the first and second electrically conductive elements24′, 26′ can be arranged in different planes, one above the electroopticwaveguide 32′ and the other below the electrooptic waveguide 32. Inaddition, as is illustrated in FIGS. 16 and 17, the first and secondelectrically conductive elements 24′, 26′ can be are arranged to overlapin the active region 15′ of the antenna assembly.

It is contemplated that the fabrication approach illustrated in FIGS. 16and 17 can lead to an enhanced response of the EO polymer modulator tothe millimeter wave, improving the responsiveness of the antenna. Thisenhanced response can result from both improved poling of theelectrooptic material and stronger interaction between themillimeter-wave electric field and the electrooptic material. Theassembly of FIGS. 16 and 17 can be fabricated by forming the lowerelectrode 26′ on the substrate 42′, applying the lower cladding 44′,forming the waveguide core 35′, applying the electrooptic layer 38′ andthe upper cladding 44′, and finally forming the upper electrode 24′ ofthe tapered slot antenna 20′. The present inventors have recognized thatmany current electrooptic polymers have better electrooptic responsewhen poled by parallel plate electrodes, as compared to coplanarelectrodes. Accordingly, at this point, the electrooptic material can bepoled, if required for the EO response, using conventional or othersuitable, yet to be developed poling conditions for the EO material.

The total thickness of the claddings and electrooptic layer is typicallyin the range of 5 to 25 microns, although other thicknesses are withinthe scope of the present invention. When the millimeter-wave radiationis first incident on the antenna, the electric field is polarized alongthe X-axis in FIGS. 16 and 17. However, as the millimeter-wavepropagates along the antenna 20′, the polarization of the electric fieldis rotated until the field is polarized in the Z-direction in the activeregion 15′. In the active region, because the millimeter-wave is moretightly confined to the cladding and electrooptic material, the velocityof the millimeter-wave signal is determined by the effective dielectricconstant of these combined layers.

In applications of the present invention where TM light does not guidein the waveguide 32′ until after the device has been poled, additionalmetal can be added on the substrate surface to allow for poling of thecomplete length of the waveguide 32′. For simplicity, the waveguide canbe routed to exit the device on the same side as which it entered,although this is not a requirement. The device is fabricated by firstforming the lower electrode 26′ on the base layer 42′, applying thelower cladding 44′, forming the waveguide core 35′ and the electroopticlayer 38′, then the upper cladding 44′. After the upper cladding 44′ isplaced on the device, a set of poling electrodes is formed over thewaveguide 32′ and the electrooptic material 38′ is poled. These polingelectrodes can be removed for convenient fabrication of the upperelectrode 24′, which is subsequently formed on the upper cladding 44′.

In the configuration of FIGS. 16 and 17, where the vertical separationbetween the first and second electrically conductive elements 24′, 26′is on the order of about 5 to 25 microns, the electric field in theactive region 15′ will alter the refractive index seen by the TMpolarized light propagating in the electrooptic waveguide 32′. Theelectrodes provide a parallel plate field, which can be more efficientinteracting with the electrooptic material than the field generated withthe coplanar electrodes illustrated in FIGS. 12-15. This enhancedelectric field and the potentially smaller electrode gap candramatically enhance the response of the antenna assembly 150 tomillimeter-wave radiation.

In each of the embodiments described herein with reference to FIGS.12-17, an optical carrier signal at the optical input 34′ of thewaveguide 32′ enters the antenna slot 22′ and continues through to theactive region 15. In the active region 15, the electric field of theincident millimeter-wave (MMW) 100 interacts with the electroopticmaterial 38′ of the active region 15′ to alter the phase of the opticalsignal. The optical signal accumulates phase shift over the entirelength of the active region 15′ and propagates to the optical output 36′of the waveguide 32′, where the optical carrier is transitioned to anoptical fiber, waveguide, or other optical medium.

FIGS. 12-17 depict the active region 15′ as a phase modulatingelectrooptic modulator, where the optical signal remains in a singlewaveguide. Alternatively, it is possible to configure the active regionas a Mach-Zehnder interferometer (MZI). In this case, the optical signalwould be evenly divided between two electrooptic waveguides before oneof the arms enters the active region 15′ between the two electrodes 24′,26′ of the tapered slot antenna 20′. The second arm would remain outsidethe active region of the antenna 20′. Downstream of the active region,the two optical signals would be recombined. It is also contemplatedthat one or both of the waveguide arms could have a mechanism to alterthe phase of light propagating along that arm. The relative phasebetween the two waveguide arms could be adjusted so the MZI could be inits lowest power state. In this state, the optical carrier could bereduced by 15 or more dB, while the power contained in the sidebandswould be unaltered. Because only half the original optical powertraverses the active region, the power in the sideband would beapproximately 3 dB lower than in the phase modulator case. However,because the carrier would be reduced by much more than 3 dB, it iscontemplated that the signal to noise ratio would be greatly improvedusing the MZI configuration.

Turning now to FIGS. 18 and 19, a plurality of tapered slot antennae 20′and corresponding waveguide cores having respective input and outputportions 34′, 36′ can be arranged on a common substrate 40′. For eachtapered slot antennae 20′, the optical signal at the optical output 36′of the waveguide core includes the carrier frequency band ω_(0′) and thefrequency sidebands ω₀±ω_(m). Each of these signals can be directedthrough a frequency dependent optical filter 50′ to discriminate thefrequency sidebands ω₀±ω_(m) from the carrier frequency band ω_(0′) byseparating the frequency sidebands ω₀±ω_(m) from the optical carrierω_(0′) and directing the sidebands ω₀±ω_(m) and the optical carrierω_(0′) to individual component outputs A, B, C of one of the filteroutput ports 51′, 52′, 53′, 54′. Further waveguides, fibers, or othersuitable optical propagation media are provided downstream of the filteroutput ports 51′-54′ to direct the signals to a photodetector array orsome other type of optical sensor.

FIGS. 18 and 19 also illustrate an embodiment of the present inventionwhere the tapered slot antennae 20′ are arranged in a one ortwo-dimensional focal plane array. In addition, the waveguide cores andthe tapered slot antennae 20′ can be configured as a parallelelectrooptical circuit. In such a configuration, the output of thephotodetector array can be used to analyze the MMW signal 100 in one ortwo dimensions because the respective output 36′ of each sensor elementwithin the photodetector array will be a function of the magnitude ofthe millimeter-wave voltage input to the modulator at a positioncorresponding to the sensor element defined by the corresponding antenna20′. More specifically, as is illustrated in FIGS. 18 and 19, each ofthe tapered slot antennae 20′ arranged in the array defines an antennapixel within the focal plane array. As such, each antenna 20′ receives adistinct pixel portion of a millimeter or sub-millimeter wave signal 100incident on the focal plane array and the optical signals at therespective output portions 36′ of each waveguide will provide a sensoroutput indicative of the one or two-dimensional distribution of the MMWsignal 100.

In the case of the one-dimensional array illustrated in FIG. 18, it isnoted that the one-dimensional array of tapered slot antennae 20′ can beformed on a common substrate 40′ and a twelve or more channel AWG 50′,also formed on the common substrate 40′, can be provided to filter thesignals from all four antennae 20′ simultaneously. FIG. 19 illustrates asimilar embodiment of the present invention, with the exception that aplurality of the one-dimensional arrays illustrated in FIG. 18 arestacked to form a two-dimensional array of tapered slot antennae 20′. Inthe embodiment of FIG. 19, it is contemplated that a single AWG can beused for each one-dimensional grouping of antennae 20′ or, if desired, asingle AWG can be used to perform the filtering for the stacked antennaarray.

Although FIGS. 18 and 19 schematically illustrate the use of an arrayedwaveguide grating (AWG) as the optical filter 50′, the optical filteringfunction of the illustrated embodiment can be accomplished using avariety of technologies including Bragg grating reflective filters,wavelength-selective Mach-Zehnder filters, multilayer thin film opticalfilters, micro ring resonator filters, and directional coupler filtersthat are wavelength selective. It is further contemplated that theembodiment illustrated in FIGS. 18 and 19 is also a viable alternativewhere lithium niobate or other non-polymeric electrooptic materials areutilized in forming the waveguide 32′.

An arrayed waveguide grating is particularly useful because it is anintegrated optical device with multiple channels characterized byrelatively narrow bandwidths. In operation, an AWG will take an inputoptical signal which has multiple frequencies, and will output N evenlyspaced frequencies at different outputs. For example, an AWG with achannel spacing of 30 GHz or 60 GHz would be well-suited for a 120 GHzantenna system. The desired channel spacing of the AWG should be suchthat the frequency of the millimeter-wave is a multiple or close to amultiple of the AWG channel spacing.

Although the above discussion of the properties of AWGs focused on theuse of a single input port of the AWG, an AWG with N output ports willoften also have N input ports, each of which outputs light to all Noutput ports. For example, in the context of an 16×16 AWG (16 inputs×16outputs), each of the 16 input ports has 16 evenly spaced wavelengths oflight, with spacing of the light corresponding to the designed spacingof the AWG. If we then look at the output of a single port, we see thatthe optical output of the selected port also has the 16 individualwavelengths, but each wavelength from came from a different input port.Accordingly, as is illustrated in FIG. 18, if four distinct opticalsignals are output from four distinct optical outputs 36′ correspondingto four distinct antennae 20, each of these outputs can include anoptical carrier ω_(0′) and two sidebands ω₀±ω_(m). If these four opticalsignals are then fed into four different input ports A of the AWG, thefour optical carriers and their corresponding eight sidebands will exitfrom twelve different output ports of the AWG. Thus, a single AWG can beused to filter multiple input signals, as long as the number of inputsignals is less than the number of AWG ports divided by three (thenumber of distinct wavelength bands input at each port).

A second advantage to using an AWG as the optical filter is alsodescribed in FIG. 6. An AWG distinguishes both sidebands from itsassociated optical carrier. In contrast, a standard bandpass filterwould remove the optical carrier and one of the sidebands. Further, ifthe two sidebands are coherent, which they are in this case, they can berecombined downstream of the AWG, leading to a 3 dB increase in theoptical response over using just a single sideband.

It is noted that recitations herein of a component of the presentinvention being “configured” to embody a particular property, functionin a particular manner, etc., are structural recitations, as opposed torecitations of intended use. More specifically, the references herein tothe manner in which a component is “configured” denotes an existingphysical condition of the component and, as such, is to be taken as adefinite recitation of the structural characteristics of the component.For example, in the context of the present invention these structuralcharacteristics may include the electrical & optical characteristics ofthe component or the geometry of the component.

It is noted that terms like “preferably,” “commonly,” and “typically,”when utilized herein, should not be taken to limit the scope of theclaimed invention or to imply that certain features are critical,essential, or even important to the structure or function of the claimedinvention. Rather, these terms are merely intended to highlightalternative or additional features that may or may not be utilized in aparticular embodiment of the present invention.

For the purposes of describing and defining the present invention it isnoted that the term “substantially” is utilized herein to represent theinherent degree of uncertainty that may be attributed to anyquantitative comparison, value, measurement, or other representation.The term “substantially” is also utilized herein to represent the degreeby which a quantitative representation may vary from a stated referencewithout resulting in a change in the basic function of the subjectmatter at issue. The term “substantially” is further utilized herein torepresent a minimum degree to which a quantitative representation mustvary from a stated reference to yield the recited functionality of thesubject matter at issue.

Having described the invention in detail and by reference to specificembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims. More specifically, althoughsome aspects of the present invention are identified herein as preferredor particularly advantageous, it is contemplated that the presentinvention is not necessarily limited to these preferred aspects of theinvention. For example, although electrooptic functional regionsaccording to specific embodiments of the present invention can beselected such that the variation of the index of refraction is dominatedby an electrooptic response resulting from the Kerr Effect because KerrEffect mediums can, in specific configurations, have the capacity forsignificantly higher changes in index of refraction than mediumsdominated by the Pockels Effect, it is understood that electroopticregion may be dominated by the Pockels Effect, the Kerr Effect, or someother electrooptic effect.

It is noted that one or more of the following claims recites a portal“wherein the structure of the portal is such that at least the followingconditions apply.” For the purposes of defining the present invention,it is noted that this phrase is introduced in the claims as anopen-ended transitional phrase that is used to introduce a recitation ofa series of characteristics of the structure and should be interpretedin like manner as the more commonly used open-ended preamble term“comprising.”

1. A millimeter or sub-millimeter wave portal system comprising anelectrooptic source and a millimeter or sub-millimeter wave detector,wherein the structure of the portal is such that at least the followingconditions apply: the electrooptic source comprises an optical signalgenerator, optical circuitry, and an optical/electrical converter; theoptical signal generator is configured to generate a modulated opticalsignal characterized by a modulation frequency of at least about 30 GHz;the optical circuitry is configured to direct the modulated opticalsignal to the optical/electrical converter; the optical/electricalconverter is configured to convert the modulated optical signal to amillimeter or sub-millimeter wave and direct the millimeter orsub-millimeter wave in the direction of an object positioned within afield-of-view defined by the millimeter or sub-millimeter wave detector;and the millimeter or sub-millimeter wave detector is configured toconvert reflections of the millimeter or sub-millimeter wave from theobject to signals representing attenuation of the millimeter orsub-millimeter wave upon reflection from the object.
 2. A system asclaimed in claim 1 wherein the optical signal generator comprises anelectrooptic sideband generator and an optical filter.
 3. A system asclaimed in claim 2 wherein: the electrooptic sideband generator isconfigured to generate frequency sidebands about a carrier frequency ofan input optical signal; and the optical filter is configured todiscriminate between the frequency sidebands and the carrier frequency.4. A system as claimed in claim 3 wherein the optical signal generatorfurther comprises optical circuitry configured to direct particularsidebands of interest to an optical output in the form of a millimeterwave optical signal.
 5. A system as claimed in claim 2 wherein: thesideband generator comprises a phase modulator comprising an opticalwaveguide and a modulation controller configured to drive the sidebandgenerator at a control voltage substantially larger than V_(π) togenerate frequency sidebands about a carrier frequency of the opticalsignal, where V_(π) represents the voltage at which a π phase shift isinduced in the optical waveguide; and the optical filter is configuredto discriminate between the frequency sidebands and the carrierfrequency such that sidebands of interest can be directed to the opticaloutput of the optical signal generator.
 6. A system as claimed in claim2 wherein: the sideband generator is formed over a device substrate andis configured to generate frequency sidebands about a carrier frequencyof the optical signal; and the optical filter is formed over the devicesubstrate and is configured to discriminate between the frequencysidebands and the carrier frequency such that sidebands of interest canbe directed to the optical output.
 7. A system as claimed in claim 2wherein the electrooptic sideband generator comprises an electroopticinterferometer and the optical filter comprises an arrayed waveguidegrating.
 8. A system as claimed in claim 7 wherein the optical circuitryis configured to combine selected optical outputs of the arrayedwaveguide grating to create the modulated optical signal.
 9. A system asclaimed in claim 1 wherein the optical circuitry is configured to directthe modulated optical signal to a plurality of optical/electricalconverters.
 10. A system as claimed in claim 9 wherein the opticalcircuitry directs the modulated optical signal to a plurality ofoptical/electrical converters by splitting the modulated optical signalinto a plurality of modulated outputs.
 11. A system as claimed in claim9 wherein the optical circuitry directs the modulated optical signal toa plurality of optical/electrical converters by redirecting themodulated optical signal sequentially from one optical/electricalconverter to the next.
 12. A system as claimed in claim 1 wherein: theoptical signal generator comprises a plurality of optical outputscharacterized by distinct frequencies; and the optical circuitry isconfigured to permit the selection and combination of different ones ofthe distinct-frequency optical outputs of the optical signal generator.13. A system as claimed in claim 12 wherein the optical circuitry isconfigured to direct different combinations of the distinct-frequencyoptical outputs to a common optical/electrical converter.
 14. A systemas claimed in claim 12 wherein the optical circuitry is configured todirect different combinations of the distinct-frequency optical outputsto plurality of different optical/electrical converters.
 15. A system asclaimed in claim 1 wherein the optical circuitry is configured to encodethe modulated optical signal prior to direction to theoptical/electrical converter.
 16. A system as claimed in claim 1 whereinthe detector comprises an antenna assembly comprising an antenna portionand an electrooptic waveguide portion.
 17. A system as claimed in claim16 wherein: the antenna portion comprises at least one tapered slotantenna; and the electrooptic waveguide portion comprises a waveguidecore extending substantially parallel to a slotline of the tapered slotantenna in an active region of the antenna assembly.
 18. A system asclaimed in claim 17 wherein: the electrooptic waveguide at leastpartially comprises a velocity matching electrooptic polymer in theactive region of the antenna assembly; a velocity v_(e) of a millimeteror sub-millimeter wave signal traveling along the tapered slot antennain the active region is at least partially a function of the dielectricconstant of the velocity matching electrooptic polymer; a velocity v_(O)of an optical signal propagating along the waveguide in the activeregion is at least partially a function of the index of refraction ofthe velocity matching electrooptic polymer; and the active region andthe velocity matching electrooptic polymer are configured such thatv_(e) and v_(O) satisfy the following relation:$\frac{{v_{e} - v_{O}}}{v_{O}} \leq {20{\%.}}$
 19. A system asclaimed in claim 16 wherein: the antenna portion comprises at least onetapered slot antenna; the waveguide portion comprises at least oneelectrooptic waveguide comprising a waveguide core in an active regionof the antenna assembly; and the electrooptic waveguide at leastpartially comprises a velocity matching electrooptic polymer in theactive region of the antenna assembly.
 20. A system as claimed in claim19 wherein: a velocity v_(e) of a millimeter or sub-millimeter wavesignal traveling along the tapered slot antenna in the active region isat least partially a function of the dielectric constant of theelectrooptic polymer; a velocity v_(O) of an optical signal propagatingalong the waveguide in the active region is at least partially afunction of the index of refraction of the electrooptic polymer; thetapered slot antenna comprises first and second electrically conductiveelements arranged to define a radiating slot of the antenna; the firstelectrically conductive element is arranged in a plane above theelectrooptic waveguide; and the second electrically conductive elementis arranged in a plane below the electrooptic waveguide.
 21. A system asclaimed in claim 1 wherein: the detector comprises an antenna assemblycomprising an antenna portion, a waveguide portion, and a frequencydependent filter; the antenna portion comprises at least one taperedslot antenna; the waveguide portion extends along at least a portion ofan optical path between an optical input and an optical output of theantenna assembly; the waveguide portion comprises a waveguide core in anactive region of the antenna assembly; the tapered slot antenna and theelectrooptic waveguide are configured such that the millimeter orsub-millimeter wave signal traveling along the tapered slot antenna isimparted on the optical signal as frequency sidebands of an opticalcarrier frequency; and the frequency-dependent filter comprises aplurality of filter output ports and is configured to discriminate thefrequency sidebands from the carrier frequency band in an optical signalpropagating along the waveguide portion, downstream of the active regionsuch that frequency sidebands having wavelengths that are shorter andlonger than a wavelength of the carrier band can be recombined at theoptical output of the antenna assembly.
 22. A system as claimed in claim1 wherein: the millimeter or sub-millimeter wave portal system comprisesa plurality of parallel portals; and each of the parallel portalscomprises at least one dedicated optical/electrical converter fed by theoptical signal generator.
 23. A system as claimed in claim 1 wherein themillimeter or sub-millimeter wave portal system comprises at least oneportal configured as a walk-through portal including at least onemillimeter or sub-millimeter wave component and a supplemental detectioncomponent.
 24. A millimeter or sub-millimeter wave portal systemcomprising an electrooptic source and a millimeter or sub-millimeterwave detector, wherein the structure of the portal is such that at leastthe following conditions apply: the electrooptic source comprises anoptical signal generator, optical circuitry, and an optical/electricalconverter; the optical signal generator is configured to generate amodulated optical signal characterized by a modulation frequency of atleast about 30 GHz; the optical signal generator comprises anelectrooptic sideband generator configured as an electroopticinterferometer to generate frequency sidebands about a carrier frequencyof an input optical signal and an optical filter configured as anarrayed waveguide grating to discriminate between the frequencysidebands and the carrier frequency at a plurality of optical outputscharacterized by distinct frequencies; the optical signal generatorfurther comprises optical circuitry configured to combine selectedoptical outputs of the arrayed waveguide grating to create the modulatedoptical signal and direct particular sidebands of interest to a commonoptical/electrical converter or a plurality of differentoptical/electrical converters in the form of a modulated millimeter waveoptical signal; the optical circuitry is configured to direct themodulated optical signal to the optical/electrical converters bysplitting the modulated optical signal into a plurality of modulatedoutputs or redirecting the modulated optical signal sequentially fromone optical/electrical converter to the next; the optical/electricalconverter is configured to convert the modulated optical signal to amillimeter or sub-millimeter wave and direct the millimeter orsub-millimeter wave in the direction of an object positioned within afield-of-view defined by the millimeter or sub-millimeter wave detector;the millimeter or sub-millimeter wave detector comprises an antennaassembly comprising an antenna portion and an electrooptic waveguideportion and is configured to convert reflections of the millimeter orsub-millimeter wave from the object to signals representing attenuationof the millimeter or sub-millimeter wave upon reflection from theobject; the antenna portion of the antenna assembly comprises at leastone tapered slot antenna and the waveguide portion of the antennaassembly comprises at least one electrooptic waveguide comprising awaveguide core in an active region of the antenna assembly; and theelectrooptic waveguide at least partially comprises a velocity matchingelectrooptic polymer in the active region of the antenna assembly.